Here are two links to ascorbic acid:
http://www.chemistrystore.com/Ascorbic_Acid.htm
http://www.msm-msm.com/store/agora.c...scorbic%20Acid
You will need about 1/2 to 1 pound of ascorbic to 10,000 gal.
Feel free to ask any questions on the stain treatment.